brooklynwx99

If we can get the ridge to pump up a little bit more out west, watch out. Vigorous 500mb ULLs at our latitude can surprise, to say the least. Definitely worth keeping an eye on, as PNA ridges are often undermodeled at such lead times.

Long range ensemble modeling is beginning to see the favorable pattern forming for the final third of December into January. There are a couple of notable features here: 1) The strength of the blocking in N Canada into the Davis Strait and Greenland has become more intense in the past couple model runs. This is a direct result of the increase in strength of the modeled Scandinavian blocking over time. We've seen this story before, and if this comes to fruition, it will provide blocking in the AO and NAO regions. This is also a very defined signal for 300 hours out. 2) The lower than normal heights in the GoA and AK have begun to retrogress. This allows for higher than average heights in the PNA domain, which is much needed for adequate cold air into the E US. I am not worried about the ridging shown over the E US here, as long range modeling has overdone this ridging all season. There will be a period of moderation, but the SE ridge shown here will slowly wash out as time goes on, especially given the +PNA/-AO/-NAO. Also, any snowfall that occurs over the next week will help lower heights over the E US. The strong blocking shown is partly a result of the strong stratospheric warming and the subsequent perturbation of the SPV into Siberia. This displacement allows for higher heights to build into the NAO and AO regions, and since the blocking is also being driven from above, there is a higher chance of the blocking being prolonged. The warming is also becoming more prominent as we move closer to the end of the month, and this will increase the strength of the blocking signal as time goes on. As @Superstorm93 showed, the 12z EPS has the same idea with a strong SSW and resulting high latitude blocking. The lower than average heights in the S US shown by the EPS also indicate an active STJ. Overall, I am becoming more and more confident that the period from December 20 to January 10 will be an exciting one due to a much more favorable hemispheric pattern. There will be a relaxation, but it most likely last less than a week. Afterwards, the perturbation of both the TPV and SPV will lead to high latitude blocking, and the retrogression of the lower than average heights near AK will promote rising heights in the PNA domain. Buckle up.

Here's a better look at the improvements aloft from 12z. At 12z, the PVA moves offshore at about Delaware's latitude, with strong NW flow right into the NYC metro. The whole orientation of the UL trough is no good. At 18z, since the energy is more amplified out west and the NS piece is able to phase in more coherently, the 500mb winds are much more favorable. Instead of offshore flow at Delaware's latitude, the flow is due N, which allows for much more PVA into the area. Because heights are higher upstream from the trough, the confluent flow is forced farther N into SE Canada. This run wasn't a hit for the N MA, but it's exactly what you want to see if you want one to occur. Now, this storm is still a week away, and the positive changes shown here could easily be erased at 00z. However, this is a good step, and we want to see these changes continue to occur in this fashion as the week progresses. A few more ticks like this and we could really have something on our hands.

Huge changes aloft. The system traverses the S US slower, which then allows the NS piece to phase more coherently. This allows heights upstream to rise moreso than 12z. This is a very interesting development, as it helps to improve the orientation of the 500mb trough, as well as providing more energy from the NS. The confluence is also less oppressive.

There's still a pretty large discrepancy between modeling, and most of it comes down to the direction of PVA and the strength/direction of the confluent flow. The 12z CMC had a pretty favorable solution for the MA and NE regions. This is for a couple of reasons. 1) Look at the direction of the 500mb wind barbs circled. They are right up the coast, which allows for PVA into the MA and NYC metro region. PVA is extremely important in the development of precipitation because of its ability to create divergence aloft. In the same way that an ice skater spreads their arms to slow their rotation while spinning to conserve momentum, an air parcel that moves from an area of high vorticity to low vorticity will also diverge. This promotes surface convergence, which then leads to precipitation. The WAA into the colder established air mass also leads to some frontogenic forcing over S NJ and SE PA, which also leads to enhanced precipitation. 2) Look at the direction of the 500mb winds over SE Canada and N NY. They are almost completely out of the east once they reach the EC's longitude. This allows for increased expansion of precipitation due to vorticity being able to advect northward more vigorously. Now let's take a look at a much different scenario aloft, the FV3 GFS: The positive features that lead to significant snowfall in the MA and NYC metro regions on the CMC are nearly gone here. 1) Looking at the 500mb wind barbs, one can see that the PVA is completely offshore once at Delaware's latitude. This means that favorable forcing is never able to reach far enough northward, and the N MA region gets no significant precipitation. This is partly due to the trough being much less amplified. 2) The confluent flow shown on the FV3 is much less favorable for significant precipitation, as it's a strong NW flow right into the N MA. Instead of the flow being southerly at NYC's latitude, it's almost completely westerly, which destroys any chance of seeing snowfall in the area. In my opinion, this feature is the most influential. If the confluent flow remains so, there is almost no shot at significant snowfall in the NYC metro. Overall, we want to see trends toward a less hostile flow out of SE Canada along with a more amplified trough. We have seen some of these shifts over the last model cycle, and there are sure to be dramatic changes in the modeled evolution of this storm, so hang tight. It's certainly something to monitor closely. This is already a major threat for the southern MA, and it could possibly become one up north, too.

Love to see upper level venting become more pronounced as time goes on. This would encourage the development of precipitation farther northward.

Here's some perspective. Wanna know where the all-important NS vort that's heavily affecting the fate of this system is? It's attached to a ULL off the Aleutian Islands. It then has to traverse through N Alaska and most of Canada before it even enters the CONUS. That doesn't even take into consideration the mess in the CONUS itself. It is impossible for modeling to have even a slight grasp on what that piece of energy is going to do. This also fails to account for the second ULL off the WC, which is the SS part of our possible system. In other words, much will change. There is a signal, and that's pretty much all there is to say.

Since December is right around the corner and there is much ambiguity in regards to the pattern that will unfold as we enter the month, I have decided to try and shed some light on how I believe the month will evolve. Let's start with the basic observed teleconnections throughout the month of November. It appears that the NAO and AO will have negative index values, while the PNA will most likely end up very weakly positive. I made a composite map of all Decembers following a November featuring a -AO/NAO and a slightly positive PNA (<1 SD). This composite has a couple interesting features. 1) There is a stout Scandinavian blocking signal. This is crucial for both the development of higher heights into the AO/NAO regions and the increase of heat flux into the stratosphere. We have already seen the effects of Scandinavian blocking this year, as there was a strong retrograding upper level high that eventually moved over Greenland. This ULH has led to the storminess that we've seen over the last couple weeks, and it bodes very well for the rest of the winter. 2) There are lower than average heights in the S US, which is one of the defining signs of a strong STJ. This effect is already being seen in the upcoming threat; part of its possible significance is in its direct connection to the STJ. However, looking at the scale on the right, these features are not extremely strong. This means that there aren't too many defined signals here except for the Scandinavian blocking, which is off the charts. The W Canada troughing looks to occur in the near future, but I believe that it will be transient in nature as the GoA trough will retrograde to the Aleutian Islands. There were a couple of maps that caught my eye, though: The stratosphere is extremely perturbed here. This is a very defined signal for strong stratospheric warming up to 10mb, as height anomalies exceed 500m! In the second image, you can actually see the perturbation near the Aleutian Islands, and this is already being shown on ensemble guidance: This is partly a result of the heat flux provided by the Scandinavian ridging. This part of the general hemispheric pattern is essential to providing a favorable upper air configuration for both the perturbation of the TPV and SPV. I believe that there will most likely be a period of moderation around the 13th, but it will most likely be short lived. The GoA trough looks to retrograde towards the Aleutians, and the continued Scandinavian ridging will affect both the TPV and SPV; this will most likely lead to continued elevated heights in the AO and NAO regions. In summation, the 8-10th threat has merit, as its connection to the STJ along with a PNA/EPO spike will lead to a favorable atmospheric configuration. The only caveat with that threat is time; many, many variables can change at such a lead time. There will most likely be a relaxation period around the 13th, but I do not expect it to last for more than a week. Afterwards, the continued battering of the TPV and SPV will lead to a favorable pattern as we enter the final third of December. This pattern could persist into early January. In other words, get some sleep.

This setup is straight up explosive. The 12/4-6 timeframe needs to be monitored.

I think it's pretty much done at this point, I can't go over 5 minutes for the presentation so I have to keep it relatively short. Staying under the time limit was probably the toughest part about this project; I could talk about this storm for a while. Thank you for the offer though, I appreciate it!!

Hey guys! I haven't been posting much lately, but that's because of a project that I've been assigned for my METEO 300 class. The project was basically to choose an observation and analyze it using figures and formulas used throughout the semester, along with other outside sources. I decided to do my project on the Blizzard of 2016, so I'm posting my analysis here in case anyone is interested. I know that it's been a long time since, but this is a weather forum after all . I understand that some of this is calculus-based, so if you have any questions regarding the significance of formulas, ask! Any criticism is welcomed! @Newman I'm aware that you're planning on majoring in meteorology as well, and calculus helps give you a deeper understanding on some of the topics that we discuss regularly on this forum. In fact, I wouldn't be surprised if you had to do a project similar to this in one of your classes!

One of the biggest problems that I see is that the general public is completely uneducated as to how forecasts are made. Many think that meteorologists, hobbyists, and students alike just rip and read model outputs, slap some numbers and pretty colors together, and call it a forecast. However, they fail to realize the days of deliberation and collaboration that go into making a solid, thoughtful forecast that attempts to account for all atmospheric variables. Do you know how difficult to nail that every time? It is impossible. The amount of data analysis, intuition, pattern recognition, and even knowledge of more nuanced topics such as variables stemming from applied calculus (divergence, curl) needed to make an informed forecast is immense. Even if you’re distinguished in forecasting ability, the atmosphere does not care. Chaos is an intrinsic part of atmospheric science, and no matter how precise we model phenomena, it will always be that way. The sooner people realize that, the better. A busted forecast has no bearing on the skill and experience of a meteorologist. It’s just part of the game. With that being said, this storm was honestly a great learning experience. I thought that the CAD would hold strong, but not nearly for as long as it did. The anomalous snowpack in SE Canada certainly had a part to play, and all of us should be more cautious of stronger cold air than forecast moving forward. SWFEs could certainly have higher impact than normal this season.

WOW. Unreal. NYC is going to break 8" if this is correct.

Modeling has still failed to correctly estimate the strength of the cold air. The HRRR has backed off on the mixing line yet again. 700mb fgen forcing is also making its way into the NYC metro. Rates will most likely increase yet again, so places reporting sleet will probably change over to snow. Incredible.

The NYC metro is about to get blitzed by heavy returns coming from the S driven by 700mb fgen forcing yet again. What an amazing storm. Some areas of the metro will certainly push 8".